Semiconductor packaging is commonly used to house and protect integrated circuits, such as controllers, ASIC devices, sensors, etc. Semiconductor packaging should protect the integrated circuits and associated electrical connections (e.g., wire bonds, solder connections, etc.) from potentially damaging environmental conditions, such as extreme temperature variations, moisture, dust particles, etc. Packaging of sensor devices such as MEMs (micro-electromechanical systems) sensor devices presents unique challenges. MEMs devices are commonly used to measure environmental parameters such as temperature, pressure, sound, composition of atmosphere, etc. The sensor elements therefore require at least partial exposure to the exterior environment so that the environmental parameter can be accurately measured. Packaging for a MEMs device therefore must meet the dual goal of protecting the integrated circuits and associated electrical connections while exposing the sensor element(s) of the MEMs device to the exterior environment.
A variety of molded package structures are used to package semiconductor MEMs devices. For example, a pre-molded structure can used to package a MEMs device, and the cavity can be filled with a soft gel, such as a silicone gel. These gels seal and protect the circuitry and electrical connections. According to another technique, the package is molded directly on the MEMs device so as to seal and protect the MEMs device with the encapsulant material (e.g., plastic or ceramic). This may be done by transfer molding, for example. According to another technique, the encapsulant material can be partially formed around the MEMs device, with an opening or chamber exposing a sensing portion of the MEMs device. This opening or chamber can be filled with a soft silicone gel.
The above described techniques suffer from several drawbacks. For example, the gels described above can potentially damage the MEMS device and/or degrade the performance of the MEMS device. In fact, the above mentioned gels cannot be used with certain MEMs devices because the gels partially or completely block the sensor. Furthermore, the molding processes used to form the packaging structures can be costly because these processes require custom tooling for specific MEMS device geometries.